The invention relates to a method for the location-dependent registration of a mobile terminal via an air interface at a base station of a communication network, the base station broadcasting a radio station identification with primary access identification with a first periodicity and a secondary access identification with a second periodicity, in each case as a layer-2 message, at least a part of the primary access identification and, respectively, of the secondary access identification being compared in the terminal with at least a part of subscription data stored in the terminal and the terminal registering at the base station as a home terminal or, respectively, as visiting terminal in the case of a positive result of the comparison.
Such methods are used in communication networks or, respectively, communication systems having a mobile radio function or, respectively, a cordless function. Such communication networks or communication systems can be designed, for example, in accordance with the GSM standard for mobile radio networks, according to the DCS1800 standard for mobile radio networks, or in accordance with the DECT standard for cordless communication networks or communication systems. If a terminal is registered as having access authorization in such communication networks or at such communication systems, characteristic data specific to the terminal are stored in the communication system or, respectively, the communication network and characteristic data specific to the communication system or, respectively, the communication network or a base station are stored as subscription data within the terminal. In the case of terminals according to the GSM standard, within the terminal means that the subscription data are stored in a so-called SIM memory card. If this memory card is inserted in another terminal, this other terminal has access authorization with respect to the communication network. In the case of communication terminals according to the cordless standard DECT (Digital Enhanced Cordless Telecommunication), the subscription data are usually stored in a memory permanently allocated to the terminal.
In a communication system according to the DECT standard, a base station sends at regular intervals a layer-2 message with a radio station identification RFPI (Radio Fixed Part Identity) which contains at least one primary access identification PARI (Primary Access Rights Identity) and a radio station number RPN (Radio Fixed Part Number). If terminals of another network or another system are also permitted within the communication system or, respectively, the communication network, the base station also broadcasts at greater intervals the primary access rights identity of this other system or, respectively, of the other network as secondary access rights identity (SARI) as a layer-2 message. A terminal located within the radio range of a base station contains an international portable user identity (IPUI), with the aid of which the subscriber identifies himself to the network. This international portable user identity is sent by the terminal to a base station when a connection is being set up or in the case of a location registration. In addition, the terminal contains at least one portable access rights key (PARK) and one PARK length indicator PLI as subscription data. The PARK and PLI identities can be used by a terminal for determining whether it has access rights with respect to a base station or a network connected thereto. For the purpose of location registration of a mobile terminal in accordance with the DECT standard, the terminal compares the primary access rights identity PARI of a received radio fixed part identity RFPI with the portable access rights key PARK, stored in its subscription memory, in order to determine whether it is a home terminal of this base station or of the connected network. If data this is not so, the terminal compares secondary access rights identities SARI broadcast by a base station with its subscription data in order to determine whether it has access rights as a visiting terminal with respect to the base station broadcasting this secondary access rights identity. If the terminal recognizes that it has access rights, it initiates a location registration at this base station.
If a network operator of a mobile network or of a cordless network changes its primary access rights identity for whatever reasons, the DECT standard, for example, provides an updating mechanism which enables it to update the subscription data of authorized terminals via the base stations of the network. This gives rise to the problem that only the terminals which are ready to operate in a switched-on state within the transmitting/receiving range of the communication network or, respectively, of the communication system can be reached by such an updating procedure. If, a terminal is not within the transmitting/receiving range of this network or, respectively, of this system whilst the primary access rights identity of a communication network or of a communication system is being changed, the subscription data of this terminal are not updated and the terminal will no longer be able to access the network at a later time.